1. Field of the Invention
The present invention relates to an assembly for tamping ballast underneath three successive ties of a longitudinally extending track including two rails supported on a plurality of successive ties resting on the ballast, the three successive ties defining cribs therebetween, the ballast tamping assembly comprising a vertically adjustable tool carrier means, three pairs of vibratory ballast tamping tools, i.e. six tamping tools, mounted on the tool carrier means and arranged successively in the longitudinal direction of the track, each tamping tool including a tamping pick and the pairs of tamping tools being so spaced from each other in this direction that two adjacent proximal tools of the three pairs may be immersed in the ballast in each crib defined between the three successive ties and a respective distal tool may be immersed in the ballast in a respective crib adjacent each crib defined between the three successive ties. The tamping tools are connected to a crank shaft by reciprocating drives for reciprocating the tools in this direction.
2. Description of the Prior Art
A ballast tamping assembly of this type has been disclosed in Austrian patent No. 385,797, of Oct. 15, 1987. In an embodiment of the assembly illustrated in FIG. 9 of the patent, a crank shaft is mounted centrally on a tamping tool carrier and the tamping tools are connected to the crank shaft by a pair of crank arms and the reciprocating drives. Each crank arm is constituted by a bell crank lever and has a bearing ring linking the bell crank lever to the crank shaft as well as a second pivot connecting the tamping tools of a respective one of the successively arranged pairs of tamping tools to the crank arm. A third link couples each crank arm to a pivot pin mounted of the tamping tool carrier. This structure has the disadvantage that it transmits a vibratory force from the crank arm to the reciprocating drives in a complex manner and the lever arrangement is susceptible to malfunctioning.
Austrian patent No. 337,753, of Nov. 15, 1976, also discloses a ballast tamping assembly for simultaneously tamping three successive ties, and the six tamping tools are also connected to a centrally arranged crank shaft. To reciprocate the tamping tools for tamping the ballast underneath the ties, the tamping tools are pivoted to the tamping tool carrier between their ends and the pivots are horizontally displaceable in the longitudinal direction of the track. Reciprocating drives are connected to the tamping tool pivots for horizontally displacing the pivots and the upper ends of the tamping tools are connected to the crank shaft by crank arms. Because of the relatively large distance of the two distal tamping tools from the central crank shaft, the two crank arms connecting the distal tools to the crank shaft are rather long and must be quite strong.
U.S. Pat. No. 3,494,297, dated Feb. 10, 1970, discloses a ballast tamping machine comprised of two machine frames linked to each other, each machine frame carrying a ballast tamping assembly capable of simultaneously tamping two successive ties and the two assemblies being so spaced from each other in the longitudinal direction of the track that three successive ties may be tamped at the same time.
A ballast tamping assembly somewhat similar to that of Austrian patent No. 337,753 has been disclosed in Swiss patent No. 569,836, granted Oct. 15, 1974, but the assembly comprises two independent tamping tool carriers arranged successively in the longitudinal direction of the track and each carrying two adjacent proximal tamping tools and a distal tamping tool connected to a crank shaft centrally mounted on the tamping tool carrier.
U.S. Pat. No. 3,372,651, dated Mar. 12, 1968, discloses a ballast tamping assembly for simultaneously tamping two successive ties, with two successively arranged pairs of tamping tools reciprocable in a manner similar to that of Austrian patent No. 337,753, and pairs of crank arms connecting the upper ends of the tamping tools of each pair to a respective crank arm.